Controller–area network (CanBus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer.

A modern automobile may have as many as 50 electronic control units (ECU) for various subsystems. Typically the biggest processor is the engine control unit, which is also referred to as "ECU" in the context of automobiles, others are used for transmission, airbags, antilock braking, cruise control, audio systems, windows, doors, mirror adjustment, etc. Some of these form independent subsystems, but communications among others are essential. A subsystem may need to control actuators or receive feedback from sensors. The CAN standard was devised to fill this need.

The CAN bus may be used in vehicles to connect engine control unit and transmission, or (on a different bus) to connect the door locks, climate control, seat control, etc. Today the CAN bus is also used as a fieldbus in general automation environments, primarily due to the low cost of some CAN Controllers and processors.

A typical canbus wave form signal showing Can high & Can low.

Above is the signal & below is the information being transmitted.

Below is a typical example of canbus systems with 4 networks, all working at different speeds. The speed depends on how quick the system needs to work, eg engine, transmission & brakes are on a flexray network that is 10 times faster that a most net work that controls radios & aux equipment.